The reaction of some styrene oxides with diborane

Abstract

Some factors which influence the reaction of styrene oxide and related epoxides with diborane in tetrahydrofuran at 25° have been studied. Styrene oxide (2-phenyloxiran) and o- and p-methyl-styrene oxide afford essentially the 2-arylethanol. (E)-1-Phenylpropene oxide (trans-2-methyl-3-phenyloxiran) yields 76% 1-phenylpropan-2-ol and 24% 1-phenylpropanol. Indene oxide and 1,2-dihydronaphthalene oxide are both cleanly reduced to indan-2-ol and 1,2,3,4-tetrahydronaphthalen-2-ol respectively. Reduction of 2-phenylpropene oxide afforded only 15% 2-phenylpropanol and 85% of an organoborane which gave 2-phenylpropane-1,3-diol on oxidation, and (E)-2-phenylbut-2-ene oxide gave almost exclusively the corresponding 2-phenylbutane-1,3-diol. The stereochemistry of the diol products is discussed, and it is suggested that the relative stability of incipient benzyl and alkyl carbonium ions influences the mode of reaction.